Boiler structure



May 24, 1932. DRAVO BOILER STRUCTURE Filed March 5, 1951 INVENTOR Patented May 24, 1932 UNITED STATES PATE T OFFICE:

FRANCIS R. DRAVO, OF'EDGEWORTH, PENNSYLVANIA, ASSIGNOR TO THE DRAVO CON- TRACTING COMPANY, A CORPORATION OF PENNSYLVANIA 1301mm STRUCTURE Application filed March 5, 1931. Serial N'o. 520,236.

My invention relates toimprovements in tubular boilers, and consists in a modification of structure, in consequence of which'the steam generated may be delivered from the boiler at higher temperature than hitherto has been attainable.

In the accompanying drawings I show a vertical boiler of fire-tube type in which, by way of example, my invention is embodied. Fig. I is a view of the boiler in vertical section; Fig. II is a View in horizontal section, on the plane indicated at IIII, Fig. I. Fig. I is diagrammatic, in that two only of the larger number of fire-tubes are shown; omission in this respect being made for the sake of clearness of showing.

The boiler of the drawings is of general cylindrical shape, and stands in the vertical position shown. At the base, within an inner wall 1 is arranged a fire-box, and from the fire-box the fire-tubes 2 arise. The outer casing3 surrounds fire-box and tubes. Within the outer casing and above the fire-box is an inner cylindrical wall 4 which, with a transverse annular partition 5 forms an annular space encircling the space within wall 4.

WVall 4 is external of the bank of boiler tubes 2. The water inlet 6 penetrates the outer casing 3 andopens to the annular space formed by wall 4 and partition 5, andtoward the lower end of that space. An orifice 7 for the incoming water opens through wall 4 toward its upper end. Water level is preferably maintained somewhathigher than orifice 7, and at a height approximately indicated by the broken line W-L. It will be understood that water entering at 6. and overflowing through orifice 7 fills all the space within the casing and exterior to the fire-box and the tubes arising from the fire-box. The water rises, as has been said, to a level indicated at W-L. From the casing 3 at its upper end the steam is led away through connection 8. The heat of the fire, conveyed through the walls of the fire-box and of the fire-tubes, heats the enveloping water and generates steam.

In such a boiler, as hitherto built and operated, and lacking the structural features in which my invention is found, the steam which is'led off through connection 8 is 'wet steam, whose temperature does not greatly exceed the temperature of ebullition. My invention consistsin'providing, within such a boiler and within the space where the steam collects before being carried off, means forcausing the steam to flow in a winding stream and in its HOW to sweep again and again over the surfaces of the fire-tubes. In

consequence, I am enabled in some degreeto 'passageway'forthe steam is formed. Referring to Fig. of the drawings, I preferably arrange within casing 3 a shell 10 which shall more closely surround the bank of tubes 2..

The purpose, of this shell is to confine the steam, and to prevent it when on its way to the exit from passing around the bank of tubes; instead of through theme From the shell 10 the baifle plates 9 extend, and, as the drawing shows, they in succession fall short of extension completely across the space within'the shell, and in this detail they; are arranged in echelon formation, so that the: steam flows horizontally between the plates and ascends step by step from one horizontal passageway to, the next, zig-zagging through succeeding passageways. The steam enters the lowest space through orifices ll; flowing from left to right, it traverses this lowest space and ascends through the opening 12 on the right to the next higher space; in it, it flows from right to left, and'from it at the left it ascends throughopening 13 to the next higher space; and soon. Eventually the steam so flowing in a stream pas'ses out at 8, for exit 8 is in communication with the highest space formed by these baflle plates.

So confined and guided, the stream of steam sweeps repeatedly across the fire-tubes 2; there is no general mingling with the whole quantity of steam within the steam space; the stream of more highly heated steam is confined; it can flow only onward, retaining its heat. The effect is, as I have said, a super-heating of the steam in substantial and valuable degree.

Theoretical considerations aside, it is not practical so to form the orifices in thebaflie plates 9 for the passage of the fire-tubes that the fit shall be very snug. That may be done for the initial assembly; but, for purposes of replacement and repair, the tubes must be freely separable from casing'and from the baflle plates 9 which the casing carries. I have found that good results may be gained if the orifices for the tubes are formed an eighth of an inch over size. Nor is there disadvantage in this; for, while there will be some leakage of steam around the tubes from one horizontal passageway ,to another, the steam which so actually leaks through, in doing so, passes in a very thin film over the hot tube surface, and takes up heat no less efiectively than it would have done, had it circulated in the main body of the stream.

I claim as my invention: v

In a vertical boiler of fire-tube type the combination of a vertically standing cylindri'cal outer shell, an inner shell of smaller diameter and of less length than the outer, concentrically arranged within and at the upper end of the outer, the upper head of the outer shell constituting the upper head of the inner shell also, the innerrshell being provided in its lower portion with an orifice in its wall establishing communication between the spaces within the two shells, a steam delivery passageway opening from the inner shell at its upper end and penetrating the wall of the outer shell, an annular plate arranged at a lower level within the outer shell and extending from the shell wall inward, and a sleeve of smaller diameter and of less length than the outer shell rising from said plate to a level lower than the lower head of the inner shell and forming with the wall of the outer shell an annular water chamber, a water inlet opening to such water chamber in the lower part thereof, the said sleeve being orificed.

for the circulation of water at a higher level than such inlet but at a point below its own upper rim, a bank of fire tubes extending vertically through the three said concentrically arranged parts, and means within the inner shell for causing steam entering at its lower orifice to sweep transversely across such bank of tubes in its course to the steam delivery passageway.

In testimony whereof I have hereunto set my hand.

FRANCIS K. DRAVO. 

